Aftertreatment SCR Conversion Efficiency Below Threshold
The SCR system isn't reducing NOx gases effectively.
Heads up: this code wasn't in our hand-written library yet, so DiagCoach AI built this page on the fly. Double-check critical specs against service info before condemning parts.
What it means (plain English)
The SCR (Selective Catalytic Reduction) system isn’t working right to clean the exhaust, meaning it can’t cut down on harmful nitrogen oxide gases like it should.
What the computer is actually seeing
The Engine Control Module (ECM) measures the level of NOx and compares it to the expected reduction by the SCR. If the efficiency is too low—often under 90% reduction—it sets this code.
What a healthy reading looks like
The SCR should ideally reduce NOx levels by at least 90%. If NOx levels are over 0.2 g/kWh, there’s a problem with SCR efficiency.
Guided diagnostic — the DiagCoach way
Don't just throw parts at it. Walk through these in order — each step tells you whether to keep going or stop and fix what you found.
- 11. Check the DEF level—should be above 2.5 gallons and DEF quality must meet ISO 22241.
- 22. Inspect wiring and connectors from the ECM to the SCR system for damage or corrosion.
- 33. Check for any exhaust obstructions (like soot or other blockages) that might affect SCR operation.
- 44. Run a NOx sensor test; values should be within 0.01 to 0.15 g/kWh while the engine is at normal operating temperature.
- 55. If any issues found in steps 1-3, fix those, clear the fault code, and test drive to see if it returns.
Common causes
- Low DEF (Diesel Exhaust Fluid) level or poor quality DEF
- Faulty SCR catalyst
- Blocked exhaust system
- Pinched or damaged DEF injector line
- Wiring or connector issues in SCR system
Typical repair cost
$$$
Related codes
Frequently asked questions
Is it safe to drive with this code active?
It's drivable, but you may notice increased emissions and possible reduced performance.
Will this code come back after resetting?
If the underlying issue isn’t fixed, it will likely return soon after the vehicle is driven.
Why does this code sometimes pair with other fault codes?
Related issues in the DEF or SCR system can trigger multiple codes at once.
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